In the field of topical analgesics, pain relieving formulations must either be extensively tested and individually approved by the Food & Drug Administration (“FDA”), or conform to the requirements of the FDA's over-the counter monograph. The two principal odorless topical analgesic active ingredients approved for use under the FDA's monograph are capsaicin and trolamine salicylate. Capsaicin is the principal capsaicinoid in chili peppers and it activates heat and pain sensing neurons producing a burning sensation when applied to the skin. Prolonged activation of these neurons by capsaicin depletes presynaptic substance P, one of the body's neurotransmitters for pain and heat. The result appears to be that the chemical mimics a burning sensation, the nerves are overwhelmed by the influx, and are unable to report pain for an extended period of time. While the result is an effective form of pain relief for some people, many people do not readily tolerate exposure to capsaicin.
Trolamine salicylate is used as a topical pain reliever to reduce swelling and inflammation. Trolamine salicylate is not tolerated by people with allergies to salicylates such as aspirin (salicylic acid), and the FDA has indicated that trolamine salicylate will be excluded from the Final Monograph for External Analgesic Drug Products for Over-the-Counter Human Use (21 CFR part 348).
As a result, there is a need for an efficacious and odorless topical analgesic product that utilizes an FDA OTC monograph active topical analgesic ingredient. It is well known that one of the most efficacious topical analgesics in the OTC monograph is menthol, in a concentration from 1.25%-16%, but menthol has a distinct and strong odor. Camphor, in a concentration from 3%-11%, is another topical analgesic from the OTC Monograph, but it also has a strong odor. At present the odorless topical analgesic products on the market utilize trolamine salicylate, capsaicin, or the homeopathic active ingredient arnica montana. These alternatives are not adequate because trolamine salicylate will soon be excluded from the FDA OTC Monograph, capsaicin is not universally tolerated, and there are controversial and mixed results about the efficacy of homeopathic actives in topical pain relief. Methyl salicylate at high concentrations, 10-60%, may also be used under the OTC Monograph, and has a strong wintergreen odor that may need suppression for acceptable use in public situations. Methyl nicotinate is another approved external analgesic ingredient, at concentrations of 0.25-1.0%, but possesses a sweet, herbaceous, tobacco-like odor that can often be masked rather than suppressed.
Odor suppression has always been problematic, especially with products containing menthol and camphor. Previously, the odor of menthol and camphor has been masked with other fragrances, but not truly suppressed or blocked. For example the odor of a product containing 7-8% menthol could be masked or altered with essential oils like spearmint, grapefruit oil, tea tree and such. The odor of a product containing both a significant amount of menthol and camphor could be masked or altered by including essential oils like spearmint, grapefruit oil, lemon oil, cucumber oil, thyme and such. The issue with odor from products containing camphor and menthol comes from the fact that these two compounds have a very high volatility and instead of reducing or stopping these compounds from volatilizing, the essential oils or other compounds were introduced only to alter or mask the odor. There has previously been no effective technique to reduce the odor of menthol or camphor containing products by actually reducing the volatility of the ingredients.